The user manual phrases things in standard Scrivener terminology, wherein the word “document” does not refer to the entire Scrivener project, nor any collective segment of that project (such as the Draft folder, although one can think of the Draft as being “a document” in a conceptual fashion, if it will be compiled front to end as one file, this isn’t a technical description of it). A text document, how the manual uses the phrase, is specifically one single item (of any kind) in the Binder. So when it refers to the usefulness of this feature in relation to “text in longer documents”, it means specifically that, long text items that are unwieldy to scroll through given their length, that have not been broken up into smaller chunks for whatever reason.
What you are attempting to do is something the software can do, by the way, it’s just not automatic about it, instead it is extremely flexible and powerful about it. 
You can use inline annotations to put down a searchable marker in the text to tag a spot—inserting the date and time is convenient and easy for that since both have a keyboard shortcut. What I just described is achieved with Shift-Cmd-A + Shift-Opt-Cmd-D. That part right there is fundamentally very similar to the existing Text Bookmark feature—we’re just using something a little more unique and expressive than an asterisk.
How you use that marker is up to you really, but keep in mind you can load a string of text into the Find tool with Cmd-E and that Cmd-G will find the next instance of that text, all without even bringing up the Find panel. What I do myself is store the marker with the link pointing to the document. Want a master list of bookmarks with stored markers? Project References are great for that, even just a list of hyperlinks in Project Notes. And of course the technique works from other areas of the Binder as well, such as links hidden within inline annotations, and this concept even can be taken completely outside of Scrivener! You can right-click on the document you wish to refer to, copy its document link, and then paste that into say, OmniFocus and supply the marker as well. Now when you come across that To-Do item in the future, you click the link, Scrivener opens the project if necessary, opens the document within the Binder, and you have your marker ready to search for.
As you may have noticed—I use this technique quite a bit, in and out of Scrivener. 
Like I say, it’s not as automatic, but it hardly takes any effort at all to make a link like this, and naturally the concept itself is so core to computing and broadly powerful that it barely even need Scrivener in order to function. It just so happens Scrivener has a cornucopia of ways to build a web of interconnections between documents, so it works quite naturally with the concept.